Choi Yong-Seok, Park Jun-Hyoung, Ahn Jae-Pyoung, Lee Jae-Chul
Department of Materials Science and Engineering, Korea University, Seoul, 02841, South Korea.
Advanced Analysis Center, Korea Institute of Science and Technology, Seoul, 02792, South Korea.
Sci Rep. 2017 Oct 25;7(1):14028. doi: 10.1038/s41598-017-14374-0.
As opposed to the common understanding that diffusion into a cubic-structured single crystal is independent of its crystalline orientation, the diffusion of Li to crystalline Si (c-Si) is anisotropic, which acts as the major cause for the fracture of Si anodes in Li-ion batteries. Here, by conducting comprehensive/multi-scale simulation studies based on molecular dynamics and density functional theory, we elucidate how and why Li diffusion in c-Si is anisotropic. We found that Li ions diffuse to c-Si by following a particular atomic-scale space corresponding to the lowest value of the valence orbital in c-Si, causing Li ions to take a tortuous diffusion pathway. The degree of the tortuosity of the pathway differs depending on the crystallographic orientation of Si, and it acts as the major cause for anisotropic lithiation. We also develop a structural parameter that can quantitatively evaluate the orientation dependency of the lithiation of c-Si.
与普遍认为扩散到立方结构单晶中与晶体取向无关的观点相反，锂向晶体硅（c-Si）的扩散是各向异性的，这是锂离子电池中硅阳极断裂的主要原因。在此，通过基于分子动力学和密度泛函理论进行全面/多尺度模拟研究，我们阐明了锂在c-Si中扩散的方式和原因。我们发现锂离子通过遵循与c-Si中价轨道最低值相对应的特定原子尺度空间扩散到c-Si中，导致锂离子采取曲折的扩散路径。该路径的曲折程度因硅的晶体取向而异，并且它是各向异性锂化的主要原因。我们还开发了一个结构参数，该参数可以定量评估c-Si锂化的取向依赖性。
